Micro-burst ultrasonic power delivery

ABSTRACT

Phacoemulsification apparatus includes a phacoemulsification handpiece having a needle and an electrical system for ultrasonically vibrating said needle along with a power source for providing pulsed electrical power to the handpiece electrical system. Irrigation fluid is provided to the handpiece needle and aspirating fluid is removed from the handpiece needle. A determination of a voltage current phase relationship of the provided electrical power is made and in response thereto a control system varies a power level duty cycle provided to the handpiece electrical system from the power source and/or modify the aspiration flow rate. In addition, a separate input enables manual control of pulse amplitude. The control system provides a pulsed electrical power of less than 20 millisecond pulse duration.

This application is a continuation of U.S. patent application Ser. No.11/560,328, filed Nov. 15, 2006, which is a continuation of U.S. patentapplication Ser. No. 10/853,863 filed May 25, 2004, now U.S. Pat. No.7,485,106, issued Feb. 3, 2009, which is a continuation of U.S. patentapplication Ser. No. 10/085,508 filed Feb. 26, 2002, now U.S. Pat. No.6,780,165, issued Aug. 24, 2004, which is a continuation-in-part of U.S.patent application Ser. No. 09/764,814 filed Jan. 16, 2001, now U.S.Pat. No. 6,629,948, issued Oct. 7, 2003, which is a continuation-in-partof U.S. patent application Ser. No. 09/298,669 filed Apr. 23, 1999, nowU.S. Pat. No. 6,394,974, issued May 28, 2002, which is acontinuation-in-part of U.S. patent application Ser. No. 09/206,452filed Dec. 7, 1998, now abandoned, which is a continuation of U.S.patent application Ser. No. 08/787,229, filed Jan. 22, 1997, now U.S.Pat. No. 5,852,794, issued Dec. 22, 1998. Each application listedhereinabove are hereby incorporated by reference in their entirety.

The present invention is generally directed to a method and apparatusfor controlling the flow of fluid from a source to a patient and removalof fluids from the patient through a phacoemulsification handpiece aswell as controlling power provided to the phacoemulsification handpiece.

The flow of fluid to and from a patient through a fluid infusion orextraction system and power control to a phacoemulsification handpieceis critical to the procedure being performed.

A number of medically recognized techniques has been utilized for lensremoval and among these, a popular technique is phacoemulsification,irrigation and aspiration. This method includes the making of a cornealincision, and the insertion of a handheld surgical implement whichincludes a needle which is ultrasonically driven in order to emulsifythe eye lens. Simultaneously with this emulsification, a fluid isinserted for irrigation of the emulsified lens and a vacuum provided foraspiration of the emulsified lens and inserted fluids.

Currently available phacoemulsification systems include a variable speedperistaltic pump, a vacuum sensor, an adjustable source of ultrasonicpower and a programmable microprocessor with operator-selected presetsfor controlling aspiration rate, vacuum and ultrasonic power levels.

Many surgical instruments and controls in use today linearly control thevacuum or linearly control the flow of aspiration fluid. This featureallows the surgeon to precisely “dispense” or control the “speed” atwhich he/she employs, either the vacuum or the flow, but not both.However, there often are times during surgery when the precise controlof one of the variables (vacuum, aspiration rate, or ultrasonic power)is desired over the other. The experienced user, understanding therelationship between the vacuum and the flow, may manually adjust thepreset variable appropriately at the console in order to obtain anacceptable performance. However, if this adjustment is overlooked, thenthe combination of both high vacuum and high flow can cause undesirablefluidic surges at the surgical site with possible damage inflicted onthe patient.

It should be apparent that the control of handheld surgical instrumentsfor use in phaco surgery is complex. Phacoemulsifier apparatus typicallycomprises a cabinet, including a power supply, peristaltic pump,electronic and associated hardware, and a connected, multi-function andhandheld surgical implement, or handpiece, including a hollowslender-like needle tube as hereinabove described, in order to performthe phacoemulsification of the cataractous lens.

It should be appreciated that a surgeon utilizing the handheld implementto perform the functions hereinabove described requires easy andaccessible control of these functions, as well as the ability toselectively shift or switch between at least some of the functions (forexample, irrigation and irrigation plus aspiration) as may arise duringphacoemulsification surgery.

In view of the difficulty with adjusting cabinet-mounted controls, whileoperating an associated handheld medical implement, control systems havebeen developed such as described in U.S. Pat. No. 4,983,901. This patentis to be incorporated entirely into the present application, includingall specification and drawings for the purpose of providing a backgroundto the complex controls required in phacoemulsification surgery and fordescribing apparatus which may be utilized or modified for use with themethod of the present invention.

To further illustrate the complexity of the control system, reference isalso made to U.S. Pat. No. 5,268,624. This patent application is to beincorporated in the present application by this specific referencethereto, including all specifications and drawings for the purpose offurther describing the state-of-the-art in the field of this invention.

It should thus be apparent, in view of the complex nature of the controlsystem of fluids and ultrasonic power in the case of phacoemulsificationprocedures, that it is desirable for a surgeon to have a system which isprogrammable to serve both the needs of the surgical procedure andparticular techniques of the surgeon, which may differ depending on theexperience and ability of the surgeon.

The present invention more specifically relates to power control to aphacoemulsification handpiece based on the determination of the phaseangle between voltage applied to a handpiece piezoelectric transducerand the current drawn by the piezoelectric transducer and/or theamplitude of power pulses provided to the handpiece.

Phacoemulsification systems typically include a handpiece having anultrasonically vibrated hollow needle and an electronic controltherefor.

As is well known in the art, the phacoemulsification handpiece isinterconnected with a control console by an electric cable for poweringand controlling the piezoelectric transducer and tubing for providingirrigation fluid to the eye and withdrawing aspiration fluid from an eyethrough the handpiece.

The hollow needle of the handpiece is typically driven or excited alongits longitudinal axis by the piezoelectric effect in crystals created byan AC voltage applied thereto. The motion of the driven crystal isamplified by a mechanically resonant system within the handpiece, suchthat the motion of the needle connected thereto is directly dependentupon the frequency at which the crystal is driven, with a maximum motionoccurring at a resonant frequency.

The resonant frequency is dependent, in part upon the mass of the needleinterconnected therewith, which is vibrated by the crystal.

For pure capacitive circuits, there is a 90 degree phase angle between asine wave representing the voltage applied to the handpiece and theresultant current into the handpiece. This is expressed by the angleequaling −90 degrees. For a purely inductive circuit, the phase angleequals +90 degrees and, of course, for purely resistive circuits=0.

A typical range of frequency used for phacoemulsification handpiece isbetween about 30 kHz to about 50 kHz. A frequency window exists for eachphacoemulsification handpiece that can be characterized by the handpieceimpedance and phase.

This frequency window is bounded by an upper frequency and a lowercutoff frequency. The center of this window is typically defined as thepoint where the handpiece electrical phase reaches a maximum value.

At frequencies outside of this window, the electrical phase of thehandpiece is equal to −90 degrees.

Handpiece power transfer efficiency is given by the formula (V*I)(COS).This means that the most efficient handpiece operating point occurs whenthe phase is closest to 0 degrees.

In order to maintain optimum handpiece power transfer efficiency, it isimportant to control the frequency to achieve a phase value as close tozero degrees as possible.

This goal is complicated by the fact that the phase angle of theultrasonic handpiece is also dependent on the loading of the transducerwhich occurs through the mechanically resonant system which includes theneedle.

That is, contact by the needle with tissue and fluids within the eyecreate a load on the piezoelectric crystals with concomitant change inthe operating phase angle.

Consequently, it is important to determine and measure the phase anglesat all times during operation of the handpiece in order to adjust thedriving circuitry to achieve an optimum phase angle in order to effectconstant energy transfer into the tissue by the phaco handpiece,regardless of loading effects.

Thus, it is important to provide automatic tuning of the handpieceduring its use in phacoemulsification tissue and withdrawing same froman eye. This auto tuning is accomplished by monitoring the handpieceelectrical signals and adjusting the frequency to maintain consistencywith selected parameters.

In any event, control circuitry for phacoemulsification handpiece caninclude circuitry for measuring the phase between the voltage and thecurrent, typically identified as a phase detector. However, problemsarise in the measurement of the phase shift without dependence on theoperating frequency of the phacoemulsification handpiece. That is,because, as hereinabove noted, the phase shift is dependent on theoperating frequency of the handpiece and time delay in the measurementthereof requires complex calibration circuitry in order to compensate toprovide for responsive tuning of the handpiece.

Phase detection is the process of applying two electrical periodicsignals of similar frequency into an electrical circuit that generates avoltage proportional to the time (phase) difference between the twosignals.

This voltage generated by the phase detector is then usually timeaveraged either by an electronic circuit or sampled by an A/D converterand then averaged digitally.

The averaged signal can be read by a conventional voltage meter or usedby a microprocessor as date for processing. The averaging also helps toreject electrical noise.

As was described earlier, the output of a phase detector is proportionalto the difference in time (of occurrence) to two signals. By definition,this means that while the electrical output of a conventional phasedetector is a function of the signal phase, it is also directlyproportional to the frequency of use. This means that the frequency ofuse must be known and compensated for when reading the phase detectoroutput in order to derive quantified phase values. While, as hereinabovenoted, a calibration circuit can account for the variation of thefrequency, such a circuit is usually very complex and may require theuse of a microcontroller. In addition, neither of these approachesaccount for the drift in performance over time which is typical ofphacoemulsification handpieces.

This problem was recognized in U.S. Pat. No. 5,431,664, which provided asolution by using the admittance of the transducers as the tuningparameter rather than the phase-angle. The necessary circuitry is, ofcourse, complicated and accordingly there is still a continuing need fora method for determining real time electrical phase for a piezoelectricphacoemulsification handpiece which is consistent over the entirehandpiece range of operation which does not require further calibrationcircuitry for the controller.

The ultrasonically driven needle in a phaco handpiece becomes warmduring use and such generated heat is for the most part dissipated bythe irrigation/aspiration fluids passing through the needle. However,care must be taken to avoid overheating of eye tissue duringphacoemulsification.

Interrupted power pulse methods have been developed in order to drivethe needle with reduced heating to avoid overheating and burning oftissue. The present invention improves this power pulse method.

SUMMARY OF THE INVENTION

In accordance with the present invention, phacoemulsification apparatusgenerally includes a phacoemulsification handpiece having a needle andan electrical means for ultrasonically vibrating the needle. The powersource provides a means for supplying pulsed electrical power to thehandpiece electrical means and a means for providing irrigation to theeye and aspirating fluid from the handpiece needle is also incorporatedin the present invention.

Input means is provided for enabling a surgeon to select an amplitude ofthe electrical pulse. Control means is provided for controlling a pulseduty cycle. In that regard, a controlled off duty cycle is establishedby the control means in order to ensure heat dissipation before asubsequent pulse is activated. Preferably the control means provides apulse of less than 20 milliseconds or a repetition rate of between about25 and about 2000 pulses per second.

In another embodiment of the present invention, a means for determiningthe voltage current phase relationship of the provided electrical poweris provided.

In this embodiment, the control means is responsive to both the pulseamplitude and the determined voltage current phase relationship forvarying a pulse duty cycle of the power supply to the handpiece.

The means for determining the voltage current phase relationshipgenerally includes the means for obtaining an AC voltage signalcorresponding to the operating AC voltage of a piezoelectric handpieceand means for obtaining an AC current signal corresponding to theoperating AC current of the piezoelectric handpiece.

Means are provided for determining the onset of a current cycle from theAC current signal and means are also provided for producing a voltage(V.sub.I) corresponding to a time necessary for the AC current to reacha maximum value after onset of the current cycle.

Additionally, means are provided for producing a voltage (V.sub.v)corresponding to a time necessary for the AC voltage to reach a maximumvalue after onset of the current cycle.

An A/D converter provides a means for comparing (V.sub.v) and (V.sub.I)to determine the phase relationship between the voltage and current ofthe piezoelectric phacoemulsification handpiece and generating a phasesignal (S.sub.p) corresponding thereto, the phase signal being frequencyindependent.

A method in accordance with the present invention for operating aphacoemulsification system which includes a phacoemulsificationhandpiece, and an ultrasonic power source, a vacuum source, a source ofirrigating fluid, and a control unit having a vacuum sensor forcontrolling the aspiration of the irrigating fluid from the handpiece.The method includes the steps of placing the handpiece in an operativerelationship with an eye for phacoemulsification procedure and supplyingirrigation fluid from the irrigation fluid source into the eye.

Pulsed ultrasonic power is provided from the ultrasonic power source tothe handpiece for performing the phacoemulsification procedure.Preferably the pulsed power of a duration of less than 20 millisecondsor at a repetition rate of between 25 and about 2000 pulses per second.

A vacuum is applied from the vacuum source to the handpiece to aspiratethe irrigating fluid from the eye through the handpiece at a selectedrate.

An input is provided enabling manual selection of power pulse amplitude.

A voltage current phase relationship of the power from the power sourcemay be determined and in response thereto, the ultrasonic power beingprovided to the handpiece is variably controlled.

In one embodiment of the present invention, the variable control of thepower includes varying the pulse duty cycle of the supply power inresponse to the pulse amplitude and/or voltage current phaserelationship.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages and features of the present invention will be betterunderstood by the following description when considered in conjunctionwith the accompanying drawings in which:

FIG. 1 is a functional block diagram of a phacoemulsification system inaccordance with the present invention;

FIG. 2 is a functional block diagram of an alternative embodiment of aphacoemulsification system in accordance with the present inventionwhich includes apparatus for providing irrigation fluid at more than onepressure to a handpiece;

FIG. 3 is a flow chart illustrating the operation of theoccluded-unoccluded mode of the phacoemulsification system with variableaspiration rates;

FIG. 4 is a flow chart illustrating the operation of theoccluded-unoccluded mode of the phacoemulsification system with variableultrasonic power levels;

FIG. 5 is a flow chart illustrating the operation of a variable dutycycle pulse function of the phacoemulsification system;

FIG. 6 is a flow chart illustrating the operation of theoccluded-unoccluded mode of the phacoemulsification system with variableirrigation rates;

FIG. 7 is a plot of the 90 degree phase shift between the sine waverepresentation of the voltage applied to a piezoelectricphacoemulsification handpiece and the resultant current into thehandpiece;

FIG. 8 is a plot of the phase relationship and the impedance of atypical piezoelectric phacoemulsification handpiece;

FIG. 9 is a block diagram of improved phase detector circuitry suitablefor performing a method in accordance with the present invention;

FIG. 10 is a plot of phase relationship as a function of frequency forvarious handpiece/needle loading;

FIG. 11 is a function block diagram of a phase controlphacoemulsification system utilizing phase angles to controlhandpiece/needle parameters with max phase mode operation;

FIG. 12 is a function block control diagram of a phase controlphacoemulsification system utilizing phase angles to controlhandpiece/needle parameters with a load detect method; and

FIG. 13 is a function block control diagram of a pulse controlphacoemulsification system.

DETAILED DESCRIPTION OF THE DRAWINGS

Turning now to the drawings, and particularly to FIG. 1 thereof, thereis shown, in functional block diagram form, a phacoemulsification systemindicated generally by the reference numeral 10. The system has acontrol unit 12, indicated by the dashed lines in FIG. 1 which includesa variable speed peristaltic pump 14, which provides a vacuum source, asource of pulsed ultrasonic power 16, and a microprocessor computer 18that provides control outputs to pump speed controller 20 and ultrasonicpower level controller 22. A vacuum sensor 24 provides an input tocomputer 18 representing the vacuum level on the output side ofperistaltic pump 14. Suitable venting is provided by vent 26.

As hereinafter described in greater detail, a phase detector 28 providesan input to computer 18 representing a phase shift between a sine waverepresentation of the voltage applied to a handpiece/needle 30 and theresultant current into the handpiece 30. The block representation of thehandle 30 includes a typical handpiece having a needle and electricalmeans, typically a piezoelectric crystal, for ultrasonically vibratingthe needle.

The control unit 12 supplied ultrasonic power on line 32 to aphacoemulsification handpiece/needle 30. An irrigation fluid source 34is fluidly coupled to handpiece/needle 30 through line 36. Theirrigation fluid and ultrasonic power are applied by handpiece/needle 30to a patient's eye which is indicated diagrammatically by block 38.Aspiration of the eye 38 is achieved by means of the control unitperistaltic pump 14 through lines 40 and 42. A switch 43 disposed on thehandpiece 30 may be utilized as a means for enabling a surgeon to selectan amplitude of electrical pulses to the handpiece via the computer 18,power level controller 22 and ultrasonic power source 16 as hereinafterdiscussed. It should be appreciated that any suitable input means, suchas, for example, a foot pedal (not shown) may be utilized in lieu of theswitch 43.

The computer 18 responds to preset vacuum levels in output line 42 fromperistaltic pump 14 by means of signals from the previously mentionedvacuum sensor 24. Operation of the control unit in response to theoccluded-unoccluded condition of handpiece 30 is shown in the flowdiagram of FIG. 3.

As shown in FIG. 3, if the handpiece aspiration line 40 is occluded, thevacuum level sensed by vacuum sensor 24 will increase. The computer 18has operator-settable limits for aspiration rates, vacuum levels andultrasonic power levels. As illustrated in FIG. 3, when the vacuum levelsensed by vacuum sensor 24 reaches a predetermined level as a result ofocclusion of the handpiece aspiration line 40, computer 18 instructspump speed controller 20 to change the speed of the peristaltic pump 14which, in turn, changes the aspiration rate. It will be appreciatedthat, depending upon the characteristics of the material occludinghandpiece/needle 30, the speed of the peristaltic pump 14 can either beincreased or decreased. When the occluding material is broken up, thevacuum sensor 24 registers a drop in vacuum level, causing computer 18to change the speed of peristaltic pump 14 to an unoccluded operatingspeed.

In addition to changing the phacoemulsification parameter of aspirationrate by varying the speed of the peristaltic pump 14, the power level ofthe ultrasonic power source 16 can be varied as a function of theoccluded or unoccluded condition of handpiece 30. FIG. 4 illustrates inflow diagram form the control of the ultrasonic power source power levelby means of computer 18 and power level controller 22. It will beappreciated that the flow diagram of FIG. 4 corresponds to the flowdiagram of FIG. 3 but varies the phacoemulsification parameter of theultrasonic power level.

With reference to FIG. 5, there is shown a flow diagram depicting thecontrol of the ultrasonic power source 16 to produce varying pulse dutycycles as a function of selected power levels. Each power pulse may havea duration of less than 20 milliseconds. As shown in FIG. 5, and by wayof illustration only, a 33% pulse duty cycle is run until the powerlevel exceeds a preset threshold; in this case, 33%. At that point, thepulse duty cycle is increased to 50% until the ultrasonic power levelexceeds a 50% threshold, at which point the pulse duty cycle isincreased to 66%. When the ultrasonic power level exceeds 66% threshold,the power source is run continuously, i.e., a 100% duty cycle. Althoughthe percentages of 33, 50 and 66 have been illustrated in FIG. 5, itshould be understood that other percentage levels can be selected aswell as various duty cycles to define different duty cycle shift points.Importantly, the pulse duration may be less than 20 milliseconds. Thisadvanced control along with the tracking mechanism herein describedenables bursts of energy less than 20 milliseconds in duration. Thiscontrol is effective in providing rapid pulse phaco power for burn freesurgery.

With reference to FIG. 13, when the computer 18 has been enabled forpulse mode operation via the switch 43, the use of thermal tissue damageis reduced. In accordance with the present invention, very rapid pulseduration of less than 20 milliseconds is provided with adequate energyto cut the tissue with kinetic or mechanical energy but then the pulseis turned off long enough to eliminate the thermal BTU's before the nextpulse is activated.

A surgeon may vary the pulse amplitude in a linear manner via the switch43 and the control unit in response to the selected pulse amplitude,irrigation and aspiration fluid flow rates, controlling a pulse dutycycle. As hereinabove noted, an off duty duration or cycle is providedto ensure heat dissipation before a subsequent pulse is activated. Inthis way, increase amplitude will increase tip acceleration and thusBTU's for tissue damaging heat generation. That is, the surgeon can uselinear power control to select the correct acceleration necessary to cutthrough the tissue density while the control unit provides acorresponding variation in pulse width of less than 20 milliseconds and“Off time” to prevent tissue de-compensation from heat. The control unitis programmed depending on the phaco handpiece chosen (total wattage) orthe phaco tip (dimensions, weight). This use of rapid pulsing is similarto how lasers operate with very short duration pulses. Pulses may have arepetition rate of between about 25 and 2000 pulses per second.

Turning back to FIG. 2, there is shown an alternative embodiment 50 of aphacoemulsification system, in accordance with the present invention,and which incorporates all of the elements of the system 10 shown inFIG. 1, with identical reference characters identifying components, asshown in FIG. 1.

In addition to the irrigation fluid source 34, a second irrigation fluidsource 35 is provided with the sources 34, 35 being connected to theline 36 entering the handpiece/needle 30 through lines 34 a, 35 a,respectively, and to a valve 38. The valve 38 functions to alternativelyconnect line 34 a and source 34 and line 38 a and source 35 with thehandpiece/needle 30 in response to a signal from the power levelcontroller 22 through a line 52.

As shown, irrigation fluid sources 34, 35 are disposed at differentheights above the handpiece/needle 30 providing a means for introducingirrigation fluid to the handpiece at a plurality of pressures, the headof the fluid in the container 35 being greater than the head of fluid inthe container 34. A harness 42, including lies of different lengths 44,46, when connected to the support 48, provides a means for disposing thecontainers 34, 35 at different heights over the handpiece/needle 30.

The use of containers for irrigation fluids at the various heights isrepresentative of the means for providing irrigation fluids at differentpressures, and alternatively, separate pumps may be provided with, forexample, separate circulation loops (not shown) which also can provideirrigation fluid at discrete pressures to the handpiece/needle 30 upon acommand from the power controller 22.

With reference to FIG. 5, if the handpiece aspiration line 38 isoccluded, the vacuum level sensed by the vacuum sensor 24 will increase.The computer 18 has operator-settable limits for controlling which ofthe irrigation fluid supplies 32, 33 will be connected to the handpiece30. It should be appreciated that while two irrigation fluid sources, orcontainers 32, 33 are shown, any number of containers may be utilized.

As shown in FIG. 6, when the vacuum level by the vacuum sensor 24reaches a predetermined level, as a result of occlusion of theaspiration handpiece line 38, the computer controls the valve 38 causingthe valve to control fluid communication between each of the containers34, 35 and the handpiece/needle 30.

It should be appreciated that, depending upon the characteristics of thematerial occluding the handpiece/needle 30, as hereinabove described andthe needs and techniques of the physician, the pressure of irrigationfluid provided the handpiece may be increased or decreased. As occludedmaterial 24, the vacuum sensor 24 registers a drop in the vacuum levelcausing the valve 38 to switch to a container 34, 35, providing pressureat an unoccluded level.

As noted hereinabove, it should be appreciated that more than onecontainer may be utilized in the present invention, as an additionalexample, three containers (not shown) with the valve interconnecting toselect irrigation fluid from any of the three containers, as hereinabovedescribed in connection with the FIG. 1A container system.

In addition to changing phacoemulsification handpiece/needle 30parameter as a function of vacuum, the occluded or unoccluded state ofthe handpiece can be determined based on a change in load sensed by ahandpiece/needle by way of a change in phase shift or shape of the phasecurve.

The typical range of frequencies used for phacoemulsification handpiece30 is between about 30 kHz and about 50 kHz. When the frequency appliedto the handpiece is significantly higher, or lower than resonancy, itresponds electrically as a capacitor. The representation of this dynamicstate is shown in FIG. 7 in which curve 60 (solid line) represents asine wave corresponding to handpiece 30 current and curve 62 (brokenline) represents a sine wave corresponding to handpiece 30 voltage.

The impedance of the typical phacoemulsification handpiece 30 varieswith frequency, i.e., it is reactive. The dependence of typicalhandpiece 30 phase and impedance as a function of frequency is shown inFIG. 8 in which curve 64 represents the phase difference between currentand voltage of the handpieces function frequency and curve 66 shows thechange in impedance of the handpiece as a function of frequency. Theimpedance exhibits a low at “Fr” and a high “Fa” for a typical range offrequencies.

Automatic tuning of the handpiece, as hereinabove briefly noted, istypically accomplished by monitoring the handpiece electrical signalsand adjusting the frequency to maintain a consistency with selectedparameters.

In order to compensate for a load occurring at the tip of thephacoemulsification handpiece, the drive voltage to the handpiece can beincreased while the load is detected and then decreased when the load isremoved. This phase detector is typically part of the controller in thistype of system.

In such conventional phase detectors, the typical output is a voltage asproportional to the difference in alignment of the voltage and thecurrent waveform, for example, −90 degrees as shown in FIG. 7. As shownin FIG. 8, it is important to consider that during the use of thehandpiece, the waveform is varying in phase and correspondingly theoutput waveform is also varying.

Heretofore, the standard technique for measuring electrical phase hasbeen to read a voltage that is proportional to phase and also tofrequency. This type of circuit can be calibrated for use with a singlefrequency as changing the frequency would cause the calibration data tobe incorrect.

This can also be seen with single frequency systems. The corrected phasevalue will draft due to variation in the circuit parameters.

The other typical approach is to utilize a microprocessor to compare thevalue of the phase detector output with that of a frequency detector andcompute the true phase. This approach is fairly complex and is subjectto drift of the individual circuits as well as resolution limitations.

A block diagram 70 as shown in FIG. 9 is representative of an improvedphase detector suitable for performing the method in accordance with thepresent invention. Each of the function blocks shown comprisesconventional state-of-the-art circuitry of typical design and componentsfor producing the function represented by each block as hereinafterdescribed.

The voltage input 72 and current 74 from a phacoemulsification handpiece30 is converted to an appropriate signal using an attenuator 76 on thevoltage signal to the phacoemulsification handpiece, and a current senseresistor 78 and fixed gain amplifier for the handpiece 30 current.

Thereafter, an AC voltage signal 80 and AC current signal 82 is passedto comparators 84, 86 which convert the analog representations of thephacoemulsification voltage and current to logic level clock signals.

The output from the comparator 84 is fed into a D flip flop integratedcircuit 90 configured as a frequency divide by 2. The output 92 of theintegrated circuit 90 is fed into an operational amplifier configured asan integrator 94. The output 96 of the integrator 94 is a sawtoothwaveform of which the final amplitude is inversely proportional to thehandpiece frequency. A timing generator 98 uses a clock synchronous withthe voltage signal to generate A/D converter timing, as well as timingto reset the integrators at the end of each cycle.

This signal is fed into the voltage reference of an A/D converter vialine 96.

The voltage leading edge to current trailing edge detector 100 uses a Dflip flop integrated circuit in order to isolate the leading edge of thehandpiece voltage signal. This signal is used as the initiation signalto start the timing process between the handpiece 30 voltage andhandpiece 30 current.

The output 102 of the leading detector 100 is a pulse that isproportional to the time difference in occurrence of the leading edge ofthe handpiece 30 voltage waveform and the falling edge of the handpiececurrent waveform.

Another integrator circuit 104 is used for the handpiece phase signal102 taken from the detector 100. The output 106 of the integratorcircuit 104 is a sawtooth waveform in which the peak amplitude isproportional to the time difference in the onset of leading edge of thephacoemulsification voltage and the trailing edge of the onset of thehandpiece current waveform. The output 106 of the integrator circuit 104is fed into the analog input or an A/D (analog to digital converter)integrated circuit 110.

Therefore, the positive reference input 96 to the A/D converter 110 is avoltage that is inversely proportional to the frequency of operation.The phase voltage signal 96 is proportional to the phase differencebetween the leading edge of the voltage onset, and the trailing edge ofthe current onset, as well as inversely proportional to the frequency ofoperation. In this configuration, the two signals Frequency voltagereference 96 and phase voltage 46 track each other over the range offrequencies, so that the output of the A/D converter 110 produces thephase independent of the frequency of operation.

The advantage of utilizing this approach is that the system computer 18(see FIGS. 1 and 2) is provided with a real time digital phase signalthat 0 to 255 counts will consistently represent 0 to 359 degrees ofphase.

The significant advantage is that no form of calibration is necessarysince the measurements are consistent despite the frequencies utilized.

For example, using AMPs operation frequencies of 38 kHz and 47 kHz andintegrator having a rise time of 150.times.10.sup.3V/2 and an 8 bit A/Dconverter having 256 counts, a constant ratio is maintained andvariation in frequency does not affect the results. This is shown in thefollowing examples.

Example 1 38 KHz Operation

Period of 1 clock cycle=1/F@38 KHz=26.32×10⁻⁶S

Portion of one period for I=90 degrees=26.32×10⁻⁶S/4=6.59×10⁻⁶S

Integrator output for one reference cycle=(150×10⁻³V/S)×(26.32×10⁻⁶S)=3.95 Volts

Integrator output from 90 degree cycle duration=(150)×10⁻³V/S)×(6.5×10⁻⁶ S)=0.988 Volts

Resulting Numerical count from A/D converter=3.95 Volts/256counts=0.0154 Volts per count

Actual Number of A/C counts for 90 degrees at 38 KHz

Example 2 47 KHz Operation

Period of 1 clock cycle−1/F@47 KHz=21.28×10⁻⁶S

Integrator output for one reference cycle=(150×10³ V/S)×(21.28×10⁻⁶S)=3.19 Volts

Integrator output from 90 degree cycle duration=(150×10³ V/S)×(5.32×10⁻⁶S)=0.798 Volts

Resulting Numerical count from A/D converter=3.19 Volts/256counts=0.0124 Volts per count

Actual Number of A/D counts for 90 degrees at 47 KHz=0.798/0.0124=64counts

A plot of phase angle as a function of frequency is shown in FIG. 10 forvarious handpiece 30 loading, a no load (max phase), light load, mediumload and heavy load.

With reference to FIG. 11, representing max phase mode operation, theactual phase is determined and compared to the max phase. If the actualphase is equal to, or greater than, the max phase, normal aspirationfunction is performed. If the actual phase is less than the max phase,the aspiration rate is changed, with the change being proportionate tothe change in phase.

FIG. 12 represents operation at less than max load in which load (seeFIG. 10) detection is incorporated into the operation, a method of thepresent invention.

As represented in FIG. 11, representing max phase mode operation, if thehandpiece aspiration line 40 is occluded, the phase sensed by phasedetector sensor 28 will decrease (see FIG. 10). The computer 18 hasoperator-settable limits for aspiration rates, vacuum levels andultrasonic power levels. As illustrated in FIG. 11, when the phasesensed by phase detector 28 reaches a predetermined level as a result ofocclusion of the handpiece aspiration line 40, computer 18 instructspump speed controller 20 to change the speed of the peristaltic pump 14which, in turn, changes the aspiration rate.

It will be appreciated that, depending upon the characteristics of thematerial occluding handpiece/needle 30, the speed of the peristalticpump 14 can either be increased or decreased. When the occludingmaterial is broken up, the phase detector 28 registers an increase inphase angle, causing computer 18 to change the speed of peristaltic pump14 to an unoccluded operating speed.

In addition to changing the phacoemulsification parameter of aspirationrate by varying the speed of the peristaltic pump 14, the power leveland/or duty cycle of the ultrasonic power source 16 can be varied as afunction of the occluded or unoccluded condition of handpiece 30 ashereinabove described.

Although there has been hereinabove described a method and apparatus forcontrolling a phacoemulsification handpiece utilizing the voltagecurrent phase relationship of the piezoelectric phacoemulsificationhandpiece in accordance with the present invention, for the purpose ofillustrating the manner in which the invention may be used to advantage,it should be appreciated that the invention is not limited thereto.Accordingly, any and all modifications, variations, or equivalentarrangements which may occur to those skilled in the art, should beconsidered to be within the scope of the present invention as defined inthe appended claims.

1.-20. (canceled)
 21. A method for controlling a phacoemulsificationsystem, the system including a handpiece, ultrasonic power source, avacuum source, a source of irrigating fluid, and a control unit, themethod comprising: a) activating a phase mode control on thephacoemulsification system; b) determining an actual phase by a phasedetector sensor; c) comparing said actual phase to a maximum phase; andd) changing an aspiration rate of the phacoemulsification system whenthe actual phase is less than the maximum phase, and maintaining normalaspiration function when the actual phase is greater than or equal tothe maximum phase.
 22. The method of claim 21, further comprising inbetween steps c) and d), determining the change between the maximumphase and the actual phase.
 23. The method of claim 22, wherein thechange in aspiration rate is proportional to the change between themaximum phase and the actual phase.
 24. The method of claim 21, whereinthe change in aspiration rate is achieved by varying the speed of aperistaltic pump.
 25. The method of claim 21, further comprising inbetween steps a) and b), setting predetermined limits for aspiration,vacuum, and ultrasonic power.
 26. The method of claim 25, wherein a usersets the predetermined limits for aspiration, vacuum, and ultrasonicpower.
 27. The method of claim 21, wherein the control unit comprises acomputer and a pump speed controller, and wherein the computer isconfigured to instruct the pump speed controller to change theaspiration rate.